Proper length and function of the pectoralis minor has been repeatedly associated with optimal scapular kinematics and posture. Conversely, shortening of this muscle can cause the scapula to assume a more internally rotated and anteriorly tilted position,1,2 as well as increase forward head and thoracic kyphosis angles.1,3 Unfortunately, adaptive shortening of this muscle can be common in overhead athletes4,5 and nonathletes2 alike. Pectoralis minor shortening has been associated with shoulder pain and pathology6–9 and is therefore often targeted during preventative injury programs and various rehabilitation protocols.
Several studies have shown that gross stretching of the pectoralis minor is not effective for correcting scapular kinematics,9,10 but does result in increased muscle length2,10 and elasticity.11 These stretching techniques have focused on moving the coracoid process away from the rib cage6,12–14 via glenohumeral horizontal abduction. Unfortunately, this gross stretch may place unwanted stress on the anterior capsuloligamentous structures. Therefore, subsequent lengthening techniques should also be incorporated and at times, substituted; however, there is a paucity in research investigating more focused stretching techniques.10 The purpose of this study was to investigate the acute effects of a self-myofascial release with motion technique for improving pectoralis minor length (PML), scapular position, and glenohumeral rotation ROM among asymptomatic individuals.
Methods
Participants
A total of 21 physically active, college-aged individuals (10 females and 11 males), based on a sample of convenience, volunteered to participate in this study (Table 1). All participants were recruited from a university via flyers and word of mouth. Each shoulder of the participants was randomly assigned to either the experiment group (n = 21) or the placebo group (n = 21). Randomization was determined by free web-based instrument (Research Randomizer, Social Psychology Network, Middletown, CT). Inclusion criteria included being asymptomatic and no recent upper-extremity injury (within the past year) or any history of upper-extremity surgery. Physically active was defined as exercising a minimum of 3 days a week for a minimum of 30 minutes per workout.
Participant’s Characteristics (Mean [SD])
| Group | Age, y | Height, cm | Mass, kg |
|---|---|---|---|
| Self-mobilization (n = 21) | 20.1 (1.5) | 172.5 (9.6) | 77.7 (17.9) |
| Placebo (n = 21) | 21.0 (1.9) | 176.8 (10.9) | 82.5 (18.7) |
Instrumentation
The Pro 3600 Digital Inclinometer (SPI-Tronic, Garden Grove, CA) was used to measure glenohumeral internal rotation, external rotation, and flexion ROM. This device provides real-time digital reading of angles with respect to either a horizontal or a vertical reference. This device is accurate up to 0.1° as reported by the manufacturer. The digital inclinometer was modified using a reference line positioned along the midline of the device, which was used for proper alignment of anatomical landmarks.
For the myofascial self-mobilization group and the placebo group, the T-Dot Mobility System (Movement Guide, Inc, Meridian, ID) was used. This system is a soft-tissue mobilization tool that allows individuals to target restricted soft tissue without the assistance of a clinician. The system consists of a padded arm that can be attached to various structures to accommodate different height and angle of application considerations (Figure 1).
—T-Dot Mobility System used for self-mobilization.
Citation: Journal of Sport Rehabilitation 29, 4; 10.1123/jsr.2018-0220
Procedures
This study utilized a blinded, blocked randomized design in which participants’ shoulders were assigned to either an experimental (myofascial self-mobilization with movement) or a placebo with movement group. All participants in this study attended one testing session using a pretest–posttest design conducted in an orthopedic rehabilitation clinic. All participants provided informed consent, as approved by the Illinois State University Institutional Review Board, prior to any data collection, and the rights of all subjects were protected at all times.
Pretest and posttest measurements consisted of glenohumeral internal rotation, external rotation, and flexion ROM, as well as PML and forward scapular posture. These measurements were collected in a randomized fashion. All test measurements were collected by the principal investigator who was blinded to the group of each limb. Once the pretest measurements were obtained, participants immediately began either the self-mobilization or the placebo procedures. All posttests measurements were completed immediately following either the self-mobilization intervention or the placebo procedures.
To assess glenohumeral internal rotation ROM, all participants were positioned supine on a standard treatment table with a towel placed under the test humerus so the limb was level with the acromion process. The principal investigator stood at the side of the examination table, just superior to the participant’s test shoulder and moved the test arm into 90° of shoulder abduction and elbow flexion. This investigator stabilized the anterior acromion with a posterior force while their other hand rotated the glenohumeral joint until the end ROM was achieved. In this position, a second investigator used the digital inclinometer to measure the participant’s available amount of passive internal rotation ROM. These procedures were then repeated for external rotation.
To measure glenohumeral flexion ROM, each participant was supine with the test shoulder resting comfortably on the treatment table and positioned at the side of their body. The principal investigator stabilized the lateral border of the scapula with a posterior force while passively moving the test arm into forward flexion. At the end range of this motion, a second investigator then aligned the digital inclinometer with the humerus to determine maximum glenohumeral flexion ROM.
Intratester reliability of these ROM measurements was established a priori. A total of 24 shoulders with no history of injury or surgery were measured and reassessed a minimum of 48 hours later. Intraclass correlation coefficient and SEM values were .98 and 2.0° for internal rotation ROM, .95 and 3.0° for external rotation ROM, and .92 and 3.0° for flexion ROM, respectively.
To measure resting PML, participants stood in an upright relaxed position. The principal investigator then used a standard cloth tape measure to assess the distance between the medial-inferior angle of the scapular coracoid process and the lateral sternocostal junction with the inferior aspect of the fourth rib. To normalize the PML to each participant, the PML was divided by the participant’s height and multiplied by 100 to determine their PML index.2 Our intratester reliability for the PML index measurement showed good intraclass reliability (.85) and SEM (0.26).
To measure forward scapular posture, participants stood in a relaxed position with their backs against a wall. The principal investigator then used the double square to measure the distance between the wall and the anterior aspect of the acromion. Our a priori reliability of this technique showed good reliability with an intraclass correlation coefficient of .84 and a SEM of 4.6 mm.
Participants with limbs assigned to the self-mobilization group stood facing the T-Dot system. The height of the application arm was raised or lowered to the height level with the middle of the pectoralis minor. The participant was then instructed to lean forward so firm pressure, described as uncomfortable, but not painful, was applied to the middle of the pectoralis minor while an investigator confirmed proper application positioning (Figure 2). The middle of the pectoralis minor was previously identified and marked in pen during the PML index measurement. While constant pressure was applied to the pectoralis minor, the participant was instructed to actively move their test arm through 15 repetitions of forward flexion–extension, horizontal abduction–adduction, and internal–external rotation with their test arm in 90° of shoulder abduction and 90° of elbow flexion. The order of these motions was not randomized. The pace of each motion was controlled using a metronome, which was set so each repetition lasted 2 seconds (1-s concentric and 1-s eccentric).
—Placement of application rod for self-mobilization with motion.
Citation: Journal of Sport Rehabilitation 29, 4; 10.1123/jsr.2018-0220
Participants with limbs assigned to the placebo with motion group performed 15 repetitions each of the same shoulder motions as the self-mobilization group. However, these limbs did not receive compression of the pectoralis minor. Rather, the arm of the mobilization system was positioned over the xiphoid process with just enough compression to hold the application arm in place, but with minimal pressure.
Statistical Methods
We conducted separate 1-way analyses of covariance using SPSS Statistical Software (IBM SPSS Statistics for Windows, version 22.0; IBM Corp, Armonk, NY). Dependent variables were posttest glenohumeral ROM, PML index, and forward scapular posture. The covariates were the pretest measurements. Effect sizes were determined as a measure of clinical significance. Within-group effect size was calculated as: (posttest mean − pretest mean)/largest SD. Between-group effect size was calculated as: (experimental group mean − placebo group mean)/pooled SD. Statistical significance was set a prior at P < .05 to determine significant group differences.
Results
Prior to data interpretation, we ensured that there was no violation of the assumptions of normality, linearity, homogeneity of variances, and homogeneity of regression slopes, as well as reliable measurements of the covariate. The pretest and posttest values for glenohumeral ROM can be viewed in Table 2, whereas PML index and forward scapular posture can be found in Table 3. Following statistical adjustment of the pretest values, the self-mobilization group had significantly greater flexion ROM (7.2°, P = .01), PML index (0.4, P = .01), and forward scapular posture (4.3, P = .03) compared with the placebo group for the posttest measurements (Table 4). The between-group effect sizes for flexion ROM and PML index were small to medium and had differences greater than their respective SEMs, which suggest clinical significance. However, the difference for forward scapular posture was within 0.3 mm of the SEM and had a small effect size, so it is difficult to determine if this difference is clinically significant. No between-group differences were found for glenohumeral external rotation (P = .13) or internal rotation ROM (P = .18).
Glenohumeral Range of Motion (in Degrees)
| Measurement | Pretest | Posttest | Difference | Within-group effect size | 95% CI |
|---|---|---|---|---|---|
| Ext Rot | |||||
| Self-Mob | 108.3 (13.4) | 111.8 (14.3) | 3.5 (6.4) | 0.24 | 109.1–114.0 |
| Placebo | 107.7 (13.4) | 108.6 (14.4) | 0.9 (4.4) | 0.06 | 106.5–111.4 |
| Int Rot | |||||
| Self-Mob | 42.1 (12.1) | 46.8 (12.1) | 4.8 (6.5) | 0.39 | 44.2–51.0 |
| Placebo | 43.7 (9.3) | 45.1 (12.7) | 1.4 (8.7) | 0.11 | 41.0–47.7 |
| Flexion | |||||
| Self-Mob | 173.6 (16.6) | 179.8 (15.0) | 6.2 (8.8) | 0.37 | 175.0–182.8 |
| Placebo | 171.4 (13.3) | 170.8 (15.4) | −0.6 (9.3) | 0.04 | 167.8–175.6 |
Abbreviations: CI, confidence interval; Ext Rot, external rotation; Int Rot, internal rotation; Self-Mob, self-mobilization. Note: Values are mean (SD).
PML Index and Forward Scapular Posture (Mean [SD])
| Measurement | Pretest | Posttest | Difference | Within-group effect size | 95% CI |
|---|---|---|---|---|---|
| PML index | |||||
| Self-Mob | 7.9 (1.2) | 8.4 (1.3) | 0.5 (0.4) | 0.38 | 8.3–8.6 |
| Placebo | 8.1 (1.2) | 8.2 (1.2) | 0.2 (0.4) | 0.08 | 8.0–8.3 |
| Forward scapular posture | |||||
| Self-Mob | 150.1 (18.0) | 144.3 (17.5) | −5.7 (7.4) | 0.32 | 143.1–148.6 |
| Placebo | 153.7 (22.2) | 151.8 (19.5) | −1.9 (6.1) | 0.09 | 147.5–153.0 |
Abbreviations: CI, confidence interval; PML, pectoralis minor length; Self-Mob, self-mobilization.
Covariate-Adjusted Posttest Data (Mean [SD])
| Measurement | Self-mobilization group | Placebo group | Between-group effect size |
|---|---|---|---|
| Ext Rot ROM, deg | 111.5 (1.2) | 108.9 (1.2) | 0.18 |
| Int Rot ROM, deg | 47.6 (1.7) | 44.3 (1.7) | 0.27 |
| Flexion ROM,* deg | 178.9 (1.9) | 171.7 (1.9) | 0.47 |
| PML index* | 8.5 (.08) | 8.1 (0.8) | 0.31 |
| Forward scapular posture,* mm | 145.9 (1.4) | 150.2 (1.4) | 0.23 |
Abbreviations: Ext Rot, external rotation; Int Rot, internal rotation; PML, pectoralis minor length; ROM, range of motion.
*Statistically significant between-group difference (P < .01).
Discussion
Tightness of the pectoralis minor can occur for a variety of reasons ranging from repetitive overhead motions of sports, such as baseball and tennis,4,5 to chronically sustained aberrant postural positions, such as a slouched position.15 This tightness has been associated with shoulder pain and specific pathologies, such as subacromial impingement.6–9 Therefore, techniques that can effectively lengthen this muscle may be beneficial in the prevention and treatment of such disorders.6,9 The results of this study demonstrate that a self-myofascial release technique with motion is effective at acutely increasing glenohumeral flexion ROM, PML, and may possibly decrease forward scapular posture.
Various gross stretching techniques have been shown to improve PML and function.6,9,11,12,16–18 These techniques commonly include some variation of end-range glenohumeral horizontal abduction and scapular retraction. Unfortunately, these techniques can place anterior soft-tissue structures, such as ligaments and the capsule, at risk for excessive strain. For this reason, more focused lengthening techniques, such as those used with myofascial release, may be warranted. Williams et al10 compared the effects of a myofascial release technique and a gross stretch for improving PML and scapular kinematics in a group of college swimmers. For the gross stretch, shoulders were passively moved into end-range horizontal abduction. For the focused stretch (myofascial release), participants were positioned supine while an investigator manually grasped the belly of the pectoralis minor and then applied an anterior force (lifted the muscle belly). The focused stretch did not result in any improvements when compared with either the gross stretch or a control group; however, the gross stretch group did improve PML when compared with the controls. The results of our study show that a self-myofascial release technique with motion can acutely improve PML and function. As such, we suggest that this technique be considered when increased anterior shoulder strain is contraindicated. However, future research is needed to confirm this hypothesis.
Tightness of the PML has been associated with scapular dyskinesis1,19,20 and various postural dysfunctions.1 More specifically, the pectoralis minor index may account for up to 78% of forward scapular posture variance.21 Subsequent studies have shown that lengthening the pectoralis minor prior to performing scapular strengthening exercises produces optimal changes in scapular posture and motion, and can also increase activity of periscapular muscles, such as the upper trapezius, the lower trapezius, and the serratus anterior.16,17 The results of our study showed a statistically significant improvement in forward scapular posture for the self-mobilization group; however, these findings may not be clinically significant. Therefore, our findings cannot definitively support these previous studies.
Kebaetse et al22 reported that altered scapular posture, such as increased scapular elevation and protraction, caused by a slouched thoracic posture, results in significantly reduced shoulder abduction ROM. Other research has reported that scapular protraction may affect scapular stability resulting in decreased shoulder elevation strength.23 We hypothesized that lengthening the pectoralis minor would result in improved scapular posture and a subsequent improvement in alignment of the humeral head and glenoid, thereby improving glenohumeral ROM. However, only flexion ROM improved among the experimental group, while external and internal rotation had no changes in ROM. These could be due to a variety of reasons, most notably the involvement of subsequent glenohumeral muscles, such as tightness of the subscapularis during shoulder external rotation and the teres minor and infraspinatus during internal rotation.
As with any study, we acknowledge that there were a few limitations to our study. The amount of pressure applied by the application arm for both groups was determined subjectively. We cannot confirm that the same amount of pressure was applied for each participant. Next, we only examined the acute effects of this technique. We cannot draw a conclusion on what affects multiple applications would produce or how long the reported changes would last. Finally, the participants used in our study were asymptomatic, which provides useful information when using this technique in the prevention of injury but does not provide insight into its application among individuals with shoulder pain. Future studies should investigate the effectiveness of this technique among different patient populations and over multiple applications to determine how long improvements may be maintained.
Conclusion
The results of this study demonstrated that a self-myofascial release technique with motion is effective for acutely improving glenohumeral flexion ROM and PML. Although there was also a statistically significant increase in forward scapular posture, this improvement may not be clinically significant. Due to the common occurrence of pectoralis minor tightness, appropriate lengthening techniques are necessary to assist with proper posture, scapular positioning, and in the prevention of shoulder pain. Therefore, the technique used in this study should be considered when attempting to address this tightness. The technique may also be beneficial because it can be self-administered without the need for a clinician.
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